A Green SON (Self Organizing Network) (hereinafter, referred to as green base station) which is a next generation self organization green wireless mobile communication network has been discussed in the current 3GPP LTE standard as an important issue. Technologies for achieving green radio resource management and operative goal of environment-friendly green base station based on new principles of green base station related current issues have been raised.
Upon review of various technologies for green wireless mobile communication networks which have been recently suggested, a ‘cell zooming’ scheme has been suggested in a paper of “cell zooming for cost-efficient green cellular networks,” (Z. Niu, Y. Wu, J. Gong, and Z. Yang, IEEE Commun. Mag., vol. 48, no. 11, pp. 74-79, November 2010) to prevent a coverage hole that may be generated when a base station is turned on/off in a voice call environment.
Also, a method for turning on and off a base station in accordance with a load status of the base station has been suggested in “Base station operation and user association mechanisms for energy-delay tradeoffs in green cellular networks,” (K. Son, H. Kim, Y. Yi, and B. Krishnamachari, IEEE Journal on Selected Areas in Communications, vol. 29, no. 8, pp. 1525-1536, September 2011). Particularly, a cost minimization problem has been solved by considering both user association based on load balancing and an issue related to energy efficiency improvement through base station on/off, and simple greedy-on (GON) and greedy-off (GOFF) algorithm has been suggested as the base station on/off method. The GON (GOFF) algorithm is a method for selecting a base station BS that has the greatest effect on the network or a BS that has the smallest effect on the network when the BSs are turned on (off) and turning on (off) the selected BS, and is a centralized procedure. FIG. 1 illustrates an example of the Greedy OFF (GOFF) algorithm.
The operative technology of a green base station is preferably performed based on the SON scheme. A next generation wireless mobile communication network is being evolved to a heterogeneous network (HetNet) where a small cell, a macro cell and a femto cell, which may be installed directly by a user, coexist as a cell size is subdivided.
Complexity of the network has been increased remarkably due to transmission powers of various sizes, coverage, a femto cell that may be installed randomly, etc. Therefore, the SON network, which enables self configuration, self optimization, self healing, etc. as a type of a distributed system that may be operated in association with or independently from a centralized scheme applied to a legacy macro cell, has been actively discussed in the LTE standard.
In this respect, the centralized radio access network (C-RAN) and the SON have contrary features such as a centralized system and a distributed system but may be developed as being complementary to each other in a heterogeneous network environment, whereby studies of managing small cells such as RRH and femto cells in accordance with the SON scheme in association with the C-RAN scheme have been made.
Referring to energy consumption of network elements to increase energy efficiency of a mobile communication network, energy of 78% to 80% of an entire energy is consumed by a base station among a server, the base station and a user equipment. In view of energy consumption by the base station, 50% to 80% of power consumption of the base station is basically used for power supply, cooling, and monitoring. This may mean that energy consumed by the base station is fixed energy consumed regardless of the amount of traffic processed by the base station, and that energy consumption corresponding to the significant amount may be reduced by turning off the base station.
Moreover, it is required to identify traffic features of the current wireless mobile communication network to turn off the base station. Traffic has dynamic features statistically. A utilization of the base station is varied at a daily cycle, and fluctuates from maximum 95% to minimum 5% or less based on a peak value. In particular, the time when the utilization of the base station is reduced to 10% or less of the peak value corresponds to 30% to 40% of the entire time. Also, coverage of the base station is overlapped in a downtown area, which may be another factor that could lead to a low utilization of the base station. Based on temporal imbalance and spatial imbalance, energy efficiency may be maximized by turning off the power of the base station when the utilization of the base station is low.